When a gas, for example a petroleum gas, contains a large proportion of heavy components, i.e. of easily condensable hydrocarbons, and when this gas has to be transported, it is necessary to free it of a portion of its components in order to avoid the formation of liquid plugs which would otherwise disrupt the transportation of the gas.
On the other hand, the recovered products may be of economic interest.
The most widely used processes for achieving such separations are of three types: expansion, absorption in a solvent and cooling.
Expansion of the gas is the simplest process; it has the disadvantage of substantially decreasing the gas pressure and leads to a low recovery yield.
In the absorption processes, the gas is contacted with the solvent wherein the heavier constituents of the gas are preferentially absorbed; the solvent having an increased content in these constituents is then subjected to expansion and/or heating so as to be regenerated and rto release the absorbed constituents; certain steps of these processes, particularly the absorption and the recovery of heavy fractions, may be refrigerated by an external refrigerating cycle.
The most conventional process consists of cooling the gas by means of an external refrigerating unit; it can be performed within a wide temperature and pressure range and leads to high recovery.
The present process is particularly adapted to the treatment of a gas containing a light fraction and a heavy fraction, wherein the light fraction contains at least one light constituent from the group comprising hydrogen, nitrogen and hydrocarbons of 1 to 2 carbon atoms and the heavy fraction contains at least one heavy constituent from the group comprising hydrocarbons of 2 to 6 carbon atoms, provided that, when the light fraction contains one hydrocarbon of 2 carbon atoms, the heavy fraction contains at least one hydrocarbon having 3 to 6 carbon atoms.